Encapsulated circuit modules are known.
Encapsulated circuit modules include a substrate having wiring (such as a printed wiring board), electronic components mounted so as to be electrically connected with the wiring of the substrate, and a resin covering the substrate together with the electronic components. By covering the electronic components with the resin, encapsulated circuit modules can provide protection for electronic components and protection of electrical contacts between the electronic components and the wiring of the substrate.
Encapsulated circuit modules include electronic components as described above. Some electronic components are vulnerable to electromagnetic waves. Other electronic components emit electromagnetic waves.
In many situations where an encapsulated circuit module is actually used, the encapsulated circuit module is combined with other electronic components. Such other electronic components may be included in another encapsulated circuit module or not. Moreover, some other electronic components are vulnerable to electromagnetic waves and others emit electromagnetic waves.
When the encapsulated circuit module is actually used, it may be desired in some cases to reduce the influence of the electromagnetic waves emitted by other electronic components outside the encapsulated circuit module on the electronic components included in the encapsulated circuit module. It may also be desired in other cases to reduce the influence of the electromagnetic waves emitted by the electronic component(s) included in the encapsulated circuit module on other electronic component(s) outside the encapsulated circuit module.
From such a viewpoint, for circuit modules without having been subjected to encapsulation with a resin, a technique of surrounding the entire circuit module with a metal shield against electromagnetic waves is practically used.
An exemplified metal shield is a box formed of a thin metal plate, with one side open. When using a box, the circuit module is not usually encapsulated with a resin. The box is attached to the substrate with the edge defining the opening of the box being in contact with the substrate to enclose the electronic components and thereby to shield the electronic components.
When, however, a box is used, the height from the substrate to the upper surface of the box often becomes relatively great, and the thickness of the circuit module thus tends to be great. Where boxes are used, it takes time and cost to make these boxes. Different kinds of boxes, if prepared depending on the height of electronic components, further increase the process steps and costs required for making the boxes. As a result, the height of the box may possibly be unnecessarily great relative to the height of the electronic component(s) on the substrate.
Since the thickness of the circuit module has a great influence on the dimensions of the final product in which it is incorporated, making it smaller is of great value. Boxes, however, often increase the thickness of the circuit module.
Another technique has been suggested for encapsulated circuit modules in which a metal shield layer is formed on the surface of the resin used for encapsulation by applying a paste containing metal powder to the surface of the resin or plating such surface with a metal using a dry or wet process. The process of applying a paste and a sputtering process, which is a kind of a dry metal-plating, have been practically used. With these processes, the problem of an excessive thickness of the encapsulated circuit module can be prevented.